(1) Field of the Invention
The present invention relates to an image forming apparatus having a fixing unit, and in particular, to estimation of a power consumption level in the fixing unit.
(2) Description of the Related Art
An electrophotographic image forming apparatus such as a printer commonly has a fixing unit that includes a pressurizing roller and a fixing roller including a heater such as a halogen lamp. Such a fixing unit, when a recording sheet having an unfixed toner image formed thereon passes through a fixing nip formed between the pressurizing roller and the fixing roller by the pressurizing roller pressing against the fixing roller, heat-fixes the toner image onto the recording sheet.
Such an image forming apparatus is no exception in the demand for energy conservation growing stronger year by year. In particular, there is a demand for a structure implementable in an image forming apparatus that enables a user to accurately keep track of power consumed by the image forming apparatus.
Commonly, an image forming apparatus executes predetermined processing such as a print job while switching on and off components such as a heater included in a fixing unit and one or more motors for driving one or more photosensitive drums, rollers, etc. Here, it should be noted that components such as a motor and a heater may operate at a power consumption level (i.e., a power level) indicating greater power than a rated power level thereof, and therefore may consume more energy than regularly consumed, particularly when an inrush of a large, instantaneous current takes place upon commencement of power supply thereto (i.e., when an inrush current occurs).
When it is desired to accurately estimate an overall power consumption level of the entire image forming apparatus, such an increase in power consumption level brought about by the inrush current cannot be ignored when taking place in the heater in the fixing unit. This is since power consumed by the heater corresponds to a great proportion of power consumed by the entire image forming apparatus.
As such, it may be considered to provide the image forming apparatus with a structure where a wattmeter or the like is provided for actually measuring the increase in power consumption level brought about by the inrush current. However, the provision of such a measurement equipment to the image forming apparatus results in increased device cost.
In view of such problems, Japanese Patent Application Publication No. 2010-152210 discloses calculating the power consumption level of the heater by assuming that a certain amount of power is additionally consumed by the heater each time the heater is activated due to inflow of the inrush current to the heater and by adding a value indicating the additional power consumption to the rated power level of the heater.
By performing calculation in such a manner, the power consumption level of the heater can be estimated with higher accuracy compared to when the effect of the inrush current is not taken into consideration.
However, according to results of confirmation performed by the present inventors, the level of the inrush current flowing into the heater upon commencement of power supply differed depending upon a duration of an interval from deactivation of the heater to the activation of the heater. In fact, the present inventors determined through such confirmation that the method described in Japanese Patent Application Publication No. 2010-152210, which involves adding, each time the heater is activated, a uniform value indicating the increase in power consumption level of the heater brought about by the inrush current to the rated power level of the heater, does not enhance the accuracy of the estimation of the power consumption level of the heater by much.